O'M 



/). I) i s (' u s s i () 11. "Cold aiicsllu'sia", "cold riii^or" 

 and death by chilling-, in lionioiothcrnis and, in several 

 cases, in ]ioikilotheniis, have been atlril)nted to a specific 

 injury to the nervous system, but nothing is known of 

 the physico-chemical mechanism of this injury. Camer- 

 on and Brownlee (191.'-)) consitler the fact that an excised 

 frog's heart is more resistant to cold than the entire 

 frog, as indicating that cold must exert a special action 

 on the nervous system; the latter is intact in llie entire 

 frog and absent in the excised heart. 



Death at temperatures above the freezing point is in 

 plants probably due to a disequilibrium resulting from a 

 change in the rate of the various physiological functions, 

 in jiai'ticular, of water absorjjtion from the ground and of 

 transpiration. 



In organisms adapted to high temperatures it is in- 

 teresting to note that injury and death are due to the 

 same factor which has produced adaptation, namely a 

 change in the temperature. While high temperature, act- 

 ing gradually for a long time, modified the organism so 

 as to make it fit the new conditions, low temperature, 

 later acting al)ru]itly for a short time, exerted an inju- 

 rious or lethal action. 



While these interpretations deal almost exclusively 

 with organisinal death, the following structural changes 

 have been invoked to explain the mechanism of proto- 

 plasmic death : 



1. Chemical changes (very few specific suggestions 

 have been made) ; 



2. Changes in the velocities of interrelated chemical 

 reactions ; 



3. Impairment of the functions of elimination and con- 

 sequent accumulation of toxic products; 



4. Impairment of the functions of osmosis and permea- 

 bility ; 



5. Impairment of the functions controlling ]jrotoplas- 

 mic water relations and resulting delivdration ; 



